SPARKS: 2 (1 converted, 0 overflowed, 0 dud, 0 GC'd, 1 fizzled)

  INIT    time    0.00s  (  0.02s elapsed)

  MUT     time    1.75s  (  1.44s elapsed)

  GC      time    0.73s  (  0.14s elapsed)

  EXIT    time    0.00s  (  0.00s elapsed)

  Total   time    2.48s  (  1.60s elapsed)

...

My full command line is: ./sudoku2 sudoku17.1000.txt +RTS -N2 -s

I understand how to interpret the Total time - 2.48 seconds is the total time spent by both cores and 1.6 seconds is the running time of the program as a whole. But how should interpret the GC times? What do 0.73s and 0.14s actually represent?

This is with GHC 7.8.3, OSX 10.8.5, 64-bit Haskell Platform.